How to scale skin modifier
Another way to complete operation: hit the Space bar, start typing "skin resize"

Change your hotkey: in the User Preferences window, in the "Input" section, you can search for "skin resize" when searching by Name, that will let you assign a new (or old) keyboard shortcut for that operation.

To find what you've got assigned to Ctrl-A, search by Key Binding and type "Ctrl A", that will show everything that's bound to that combination.